Power management devices are ubiquitous in today's society and necessary to deliver power to many of the devices we use every day such as phones and laptops. Some power management devices provide electrical isolation that allows the alternating current (AC) power provided by an outlet to be converted to the direct current (DC) power used by modern computing devices while other power management devices convert one DC power level to a second DC power level. The automobile industry has been adopting power management devices with an increasing pace in recent years.
As such, power management devices have become more essential to the function of the modern automobile. A power management device may take, for example, an input voltage and convert it to a desired output voltage. The ability of a given power management device, such as a buck converter, to regulate or convert a voltage can be affected by a number of environmental factors, such as temperature.
To mitigate the impact on the functionality and lifetime of automobile power management components, many automotive manufacturers are requiring power management devices to be able to be adapted to adverse environmental conditions. One such environmental condition results in a phenomenon known as cold crank. Under cold crank conditions the input voltage (e.g., a battery voltage) of a power management device having, for example, a nominal voltage of twelve volts may drop down to as low as approximately three volts. As the input voltage recovers from the cold crank condition a large amount of current is required to bring the output voltage of the power management device to the desired output voltage. This inrush of current can overheat and damage the power management device.
Automotive manufacturers often perform input voltage step response testing to emulate a cold crank condition of the input voltage. Cold crank testing involves causing the regulation voltage on a power management device, such as a buck converter, to deviate 10% or more from the nominal regulation voltage. The expectation is for the power management device to return to nominal output voltage after recovering from a large drop in the input voltage. However, when the duty cycle of a pulse width modulated signal controlling a power management device becomes more than 90% and the output voltage of the power management device is too low, the compensation current can reach a current limit. This results in either the output voltage overshooting the nominal regulation voltage or the inductor reaching a current limit and causing the power management device to enter a hiccup mode.
A hiccup mode is an over-current protection mechanism that turns off a power management device and causes it to enter a sleep mode when the inductor current becomes too high. A hiccup mode may be implemented by using, for example, a counter to count the number of cycles for which a current limiting event has occurred, thereby forcing the power management device to enter the hiccup mode when a certain number of current limiting events have been counted. A soft start circuit is typically employed to ramp up the output voltage when the power management device is turned back on.